Bellows accumulator, in particular pulsation damper

ABSTRACT

The invention relates to a bellows accumulator, in particular a pulsation damper, comprising a bellows (3), which, arranged in an accumulator housing (1), separates two media chambers (27, 28) from each other and the bellows folds (19) of which can be moved at least partially along the inner wall (35) of the accumulator housing (1). Said bellows accumulator is characterized in that the outside diameter of the bellows folds (19) is selected to be slightly smaller than the associable diameter of the inner wall (35) of the accumulator housing (1) in such a way that spaces (37, 41) are formed, which together form a hydraulic damping means for at least one medium.

The invention concerns a bellows accumulator, in particular a pulsationdamper, comprising a bellows, which, arranged in an accumulator housing,separates two media chambers from each other, and the bellows folds ofwhich can be moved at least partially along the inner wall of theaccumulator housing.

Bellows accumulators of this kind are prior art, compare for example WO2011/079890 A1. Such bellows accumulators are preferably used inhydraulic systems as pulsation dampers in order to reduce or dampenpressure spikes that occur in hydraulic fluids. In applications wherepressure spikes occur with high frequency and the bellows are subjectedto high vibrational loads, the known bellows accumulators are at theirlimit. In particular in systems where safety is critical, such ashydraulic actuators for wing flaps or stabiliser components in aircraft,the known bellows accumulators are not able to meet the stipulatedoperational safety requirements.

Based upon this problem it is the object of the invention to provide abellows accumulator that can be used specifically as a pulsation damper,and which is characterized by a favourable operating characteristic anda particularly effective damping effect.

This object is met according to the invention by a bellows accumulatorthat has the characteristics of claim 1 in its entirety.

According to the characterizing part of claim 1 a particular feature ofthe invention is that the outer diameter of the bellows folds isselected to be slightly smaller than the associable diameter of theinner wall of the accumulator housing in such a way that interspaces areformed, which together form a hydraulic damping means for at least onemedium. With the chosen, small difference in diameter and thecorrespondingly small width of the gap formed between the outside of thebellows and the inner wall of the housing, a plurality of dampingthrottles is formed between subsequent fold gaps that correspond to thenumber of bellows folds, wherein in the instance of a bellows movement,where the volumes of the interspaces change, parts of the medium flowsthrough, which is located inside the gap and inside the interspaces.Particularly in the instance of pulsations that take place at highfrequencies and relatively low amplitudes, such as is the case withhydraulic fluid supplied by means of screw compressors, hydraulicdamping is achieved on the outside of the bellows in addition to thedamping caused by the volume changes of the bellows.

In advantageous exemplary embodiments the size of the interspaces toachieve the hydraulic damping effect is chosen such that, underconsideration of the medium in the gap, a sliding guide of the bellowsfolds is achieved in the accumulator housing in the gap between theouter diameter of the bellows and the inner diameter of the housing,since a kind of slide bearing is formed by a lubricating film of themedium if the gap is small. Advantageously, a sliding guide of this kindcan facilitate a movement of the bellows parallel to the longitudinalaxis of the accumulator housing and impedes it in the directiontransverse to the longitudinal axis. Whilst the above-described, knownsolution provides a sleeve that covers the outside of the bellows toprotect it from excessive vibrational loads that occur in operation,which sleeve is attached to the moving end of the bellows so as toprovide circumferential guidance for the bellows, the sliding guideprovided by the invention acts as a hydrostatic slide bearing. Thisprovides the bellows with protection against excessive vibrational loadswithout burdening the bellows with an additional moveable mass, such asthe sleeve in the known solution, which ensures an optimal response anddamping characteristic at high frequencies.

In advantageous exemplary embodiments the medium space between theoutside of the bellows and the associated inside of the bellows housingmay contain a medium of high viscosity, such as a phosphoric acid esteroil (HFD-R), whereas the medium on the inside of the bellows may be aprocess gas such as nitrogen gas. When using these types of media, thebellows accumulator according to the invention is particularly suitablefor aeronautical engineering applications where corresponding safetyregulations apply for the media used, such as low flammability, coldenvironment operating limits and such like.

The size or the dimension of the gap respectively may, advantageously,be between 3.0 mm and 0.15 mm, particularly preferred between 2.0 mm fora low hydraulic damping effect and 0.25 mm for an extremely highhydraulic damping effect. With the dimension of the gap chosen in thismanner, the gap between the sliding guide of a corresponding bellowsfold is transformed into damping spaces at the assignable inner wall ofthe accumulator housing at least when the bellows is extended, whereinsaid damping spaces are delimited by two adjacently located bellowsfolds.

In advantageous exemplary embodiments the height of the bellows in itsextended state may be one to one and a half times of the internaldiameter.

The bellows may, with particular advantage, be made from a metallicmaterial and/or the ends of the folds may have tapered cross-sectionsand/or the bellows does not require any additional guiding facilities inthe vicinity of its sliding guide inside the accumulator housing.

In a preferred embodiment the one end of the bellows is attached to amoveable end body, whereas the other end of the bellows is secured to aretaining ring that is fixed to the housing.

Particularly advantageously the arrangement may be such that themoveable end body closes the inside of the bellows off with respect tothe one medium connection of the accumulator housing, is circular inshape and is provided with protruding guide members for making contactwith inner wall parts of the accumulator housing, where media passagesextend between the guide members of the end body. Despite the lateralguide provided for the moveable end of the bellows, the fluid connectionto the media space between the outside of the bellows and the inside ofthe accumulator housing remains intact.

The invention will now be described in detail by way of exemplaryembodiments depicted in the drawing.

Shown are in:

FIG. 1 a longitudinal cross-section of an exemplary embodiment of thebellows accumulator according to the invention, wherein the bellows isshown fully extended;

FIG. 2 an enlarged depiction of the section marked with II in FIG. 1;and

FIG. 3 a longitudinal cross-section of a further exemplary embodiment,also with fully extended bellows.

The invention is now explained with reference to the attached drawingsby way of examples of pulsation dampers, which are particularly intendedto reduce or dampen pressure spikes, which occur at high frequencies inthe hydraulic fluid of the hydraulic system of an aircraft. FIG. 1depicts with the reference number 1 as a whole the accumulator housingof an exemplary embodiment comprising a main housing part 2, which maycontain the metallic bellows 3. The main housing part 2 is made in theform of a circular-cylindrical pot with a bottom 5, which is closedexcept for a centrally located fluid connection 7. At the opposite,upper end, as depicted in FIG. 1, the main part 2 is provided with anincreased wall thickness 9, welded to the free end of which is ametallic housing end part 13 along the weld seam 11. Said housing endpart 13 has the form of a domed cup, which is closed apart from acentrally located filling opening 15, which is closed by means of a weldnugget 17.

The metallic bellows 3 that is located inside the main part 2 is weldedat its open bellows end, shown at the top in FIG. 1, with its lastbellows fold 19 to a metallic retaining ring 21, which is provided witha thickened circumferential edge 23 with which it is secured to theaccumulator housing 1 in such a manner that the thickenedcircumferential edge 23 overlaps the weld seam 11 between main part 2and end part 13, wherein the welding method used is a full penetrationwelding process using electron-beam welding (laser welding) so that thecircumferential edge 23 of the retaining ring 21 is also welded on. Theopposite, lower end of the bellows 3 is closed by a metallic,plate-shaped bottom part 25 to which the lowest bellows fold 19 iswelded.

FIG. 1 depicts the operational state in which the bellows 3 is fullyextended and the oil end 27 is empty, wherein the associated fluidconnection 7 is closed with a protective screw cap 29. When used inaeronautical engineering systems, the bellows 3 forms the moveableseparation element between a viscous hydraulic fluid on the oil side 27,such as a phosphoric acid ester oil (HFD-R), which, as alow-flammability liquid, is permitted for aeronautical applications, anda process medium, such as a process gas, such as nitrogen gas, which ispresent on the gas side 28 of the accumulator housing 1 under apre-filing pressure, wherein said gas side 28 is formed by the innerspace of the bellows 3 as well as the housing part located above theretaining ring 21.

To facilitate the guidance of the axial movements of the bottom part 25,which changes the volume of the bellows, said bottom part 25 is guidedby a guide ring 33 disposed on its circumferential edge 31 that is madefrom a synthetic material with good sliding properties, for exampletetrafluoroethylene. In order to facilitate the passage of fluid fromthe oil side 27 that is adjacent to the fluid connection 7 to theoutside of the bellows 3 despite the axial guide provided by the guidering 33, so that also the area of the gap 37 between the outside of thebellows and the inner wall of the housing 35 is part of the oil side 27,the guide ring 33 has the shape of a flat ring that is formed in such amanner as is shown for a guide ring that fulfills a comparable functionthat is depicted in FIGS. 2 and 3 of the document WO 2011/079890 A1 andreferenced with the number 47, cited above as prior art. In accordancewith that the guide ring 33 is provided with circumferentially spaced,radially protruding guide sections that are in contact with the innerhousing wall 35 and between which are radially recessed gaps that allowthe fluid to pass through.

As is most clearly shown in FIG. 2, a gap 37 is provided between theinner wall 35 of the main part 2 of the accumulator housing 1 and theouter diameter of bellows 3 that is established by the tips of thebellows folds 19, wherein the width of said gap is indicated in FIG. 2by the arrows 39. In conjunction with the interspaces 41, which areformed between its folds 19 by an at least not fully compressed bellows3, the volumes of which change accordingly with the movement of thebellows in operation, damping spaces are formed between the outside ofthe bellows and the inner housing wall 35 as part of the oil side 27. Asis apparent from FIG. 2, damping throttles are formed between the tipsof the folds 19 and the inner housing wall 35 for the fluid flow thatresults from the volume changes of the fold interspaces 41 caused by thebellows movement in operation, wherein the chosen gap size determinesthe throttle cross-section. In addition to the pulsation damping effectdue to the movement of the bellows against the pressure cushion of theprocess gas, a hydraulic damping effect is achieved on the outside ofthe bellows. For reasons of clarity the folds 19 and the interspaces 41between the folds 19 are not all marked as such in FIGS. 1 and 2.

The size of the gap may be selected depending on the desired dampingeffect; for example a gap of 2.0 mm for a relatively low damping effector 0.25 mm for a high damping effect. With such small gap sizes and ahighly viscous medium on the oil side 27, such as phosphoric acid esteroil, a lubricating film is formed between the inner housing wall 35 andthe outside of the bellows 3, wherein said lubricating film acts asaxial guidance for the bellows folds 19 inside the housing 1 andprovides protection for the folds 19 with respect to vibrational loads.The bellows accumulator according to the invention is thus particularlysuitable as a damping device for fluids with high-frequency pressurespikes. The invention is also suitable for use in high-frequencypulsation applications because it is not necessary to attach anadditional oscillating mass to bellows 3 for the guidance of the bellowsfolds 19, as it is necessary in the above-described, known solutionwhich provides a sleeve on the bellows that surrounds the folds.

FIG. 3 depicts a modified exemplary embodiment in which the accumulatorhousing 1 is closed at the upper end of the circular-cylindrical mainpart 2 through a domed cover part 45 that is connected to main part 2.The lower end of main part 2 is closed along the weld seam 47 by a flathousing bottom 49, which corresponds to the bottom 5 of the firstexemplary embodiment and which, in likewise manner, is provided with acentral filling connection 7 for the hydraulic fluid. The metallicbellows 3 in this exemplary embodiment is open towards the bottom 49 sothat the inside of the bellows 3 forms the oil side 27. The retainingring 21, which is welded to the last bellows fold 19 at the open end ofthe bellows 3, is formed in this exemplary embodiment by a flat ring,which is fixed along the weld seam 47 to the lower end of the mainhousing part 2.

As in the first exemplary embodiment, the bottom part 25, which formsthe closed end of the bellows 3 and which is welded to the last bellowsfold 19 that faces it, is axially moveable. Again, as in the firstexemplary embodiment, the bottom part 25 is fitted at thecircumferential edge 31 with the guide ring 33 that is provided withpassages so that the gap 37, which is formed, like in the firstexemplary embodiment, between the inner housing wall 35 and the outsideof the bellows 3 and which in FIG. 2 is indicated by the gap dimension39, forms together with the interspaces 41 between the folds 19 dampingspaces, with damping throttles formed between the tips of the folds 19and the inner wall 35 for the flow of process gas when the bellows 3moves, causing volume changes of the interspaces 41. As in the firstexemplary embodiment, this causes on the outside of the bellows 3 anadditional damping effect. As in FIGS. 1 and 2, the folds 19 and theinterspaces 41 between the folds 19 shown in FIG. 3 are not all markedas such for reasons of clarity.

1. A bellows accumulator, in particular a pulsation damper, comprising abellows (3), which, arranged in an accumulator housing (1), separatestwo media chambers (27, 28) from each other, and the bellows folds (19)of which can be moved at least partially along the inner wall (35) ofthe accumulator housing (1), characterized in that the outer diameter ofthe bellows folds (19) is selected to be slightly smaller than theassociable diameter of the inner wall (35) of the accumulator housing(1) in such a way that interspaces (37, 41) are formed, which togetherform a hydraulic damping means for at least one medium.
 2. The bellowsaccumulator according to claim 1, characterized in that the size of theinterspaces (37, 41) to achieve the hydraulic damping effect is chosensuch that, under consideration of the medium in the gap (37), a slidingguide of the bellows folds (19) is achieved in the accumulator housing(1) in the gap between the outer diameter of the bellows (3) and theinner diameter (35) of the housing (1).
 3. The bellows accumulatoraccording to claim 1, characterized in that the sliding guidefacilitates a movement of the bellows (3) parallel to the longitudinalaxis of the accumulator housing (1) and impedes it in the directiontransverse to the longitudinal axis.
 4. The bellows accumulatoraccording to claim 1, characterized in that the medium space (27)between the outside of the bellows and the associated inner wall (35) ofthe accumulator housing (1) contains a medium of high viscosity, such asa phosphoric acid ester oil (HFD-R), whereas the medium on the inside ofthe bellows (28) is a medium such as nitrogen gas.
 5. The bellowsaccumulator according to claim 1, characterized in that the size of thegap (37), or the gap dimension respectively, is chosen to be between 3.0mm and 0.15 mm, particularly preferred between 2.0 mm for a lowhydraulic damping effect and 0.25 mm for an extremely high hydraulicdamping effect.
 6. The bellows accumulator according to claim 1,characterized in that the gap (37) between the sliding guide of acorresponding bellows fold (19) is transformed into damping spaces (41)at the assignable inner wall (35) of the accumulator housing (1) atleast when the bellows (3) is extended, wherein said damping spaces (41)are delimited by two adjacently located bellows folds (19).
 7. Thebellows accumulator according to claim 1, characterized in that theheight of the bellows (3) in its extended state may be one to one and ahalf times of its internal diameter.
 8. The bellows accumulatoraccording to claim 1, characterized in that the bellows (3) is made froma metallic material and/or that the ends of the folds have taperedcross-sections and/or that the bellows (3) does not require anyadditional guiding facilities in the vicinity of its sliding guideinside the accumulator housing (1).
 9. The bellows accumulator accordingto claim 1, characterized in that the one end of the bellows is attachedto a moveable end body (25), whereas the other end of the bellows (3) issecured to a retaining ring (21) that is fixed to the housing.
 10. Thebellows accumulator according to claim 1, characterized in that themoveable end body (25) closes off the inside (28) of the bellows (3)with respect to a medium connection (7) of the accumulator housing (1),is circular in shape and is provided with protruding guide members formaking contact with inner wall parts (35) of the accumulator housing(1), where media passages extend between the guide members of the endbody (25).